I repeat Sturgeon's Revelation, which was wrung out of me after twenty years of wearying defense of science fiction against attacks of people who used the worst examples of the field for ammunition, and whose conclusion was that ninety percent of it is crud.
The Revelation: Ninety percent of everything is crud.
Corollary 1: The existence of immense quantities of trash in science fiction is admitted and it is regrettable; but it is no more unnatural than the existence of trash anywhere.
Corollary 2: The best science fiction is as good as the best fiction in any field.

Venture Science Fiction (March 1958) The original expression of this has often been declared to have been "Sure, ninety percent of science fiction is crud. That's because ninety percent of everything is crud." According to Philip Klass Sturgeon made the remark during a talk at New York University around 1951. It has also commonly appeared in variant forms such as "Ninety percent of everything is crap" and is often referred to as "Sturgeon's Law" — though he himself gave that title to another phrase:

Sturgeon's Law originally was "Nothing is always absolutely so." The other thing was known as "Sturgeon's Revelation".

Interview with David G Hartwell, The New York Review of Science Fiction (March - April 1989)

A science fiction story is a story built around human beings, with a human problem and a human solution, which would not have happened at all without its scientific content.

As quoted in The Issue at Hand: Studies in Contemporary Magazine Science Fiction (1964) by James Blish, p. 14

It means "Ask the next question." Ask the next question, and the one that follows that, and the one that follows that. It's the symbol of everything humanity has ever created, and is the reason it has been created. This guy is sitting in a cave and he says, "Why can't man fly?" Well, that's the question. The answer may not help him, but the question now has been asked.
The next question is what? How? And so all through the ages, people have been trying to find out the answer to that question. We've found the answer, and we do fly. This is true of every accomplishment, whether it's technology or literature, poetry, political systems or anything else. That is it. Ask the next question. And the one after that.

Science fiction, outside of poetry, is the only literary field which has no limits, no parameters whatsoever. You can go not only into the future, but into that wonderful place called "other", which is simply another universe, another planet, another species.

Logic and truth are two very different things, but they often look the same to the mind that’s performing the logic.

Chapter 2, p. 97

Reality isn’t the most pleasant of atmospheres, Lieutenant. But we like to think we’re engineered for it. It’s a pretty fine piece of engineering, the kind an engineer can respect. Drag in an obsession and reality can’t tolerate it. Something has to give; if reality goes, your fine piece of engineering is left with nothing to operate on. So it operates badly. So kick the obsession out; start functioning the way you were designed to function.

Chapter 3 “Morality”, p. 146

Love’s a different sort of thing, hot enough to make you flow into something, interflow, cool and anneal and be a weld stronger than what you started with.

The most human thing about anyone is a thing he learns and … and earns. It’s a thing he can’t have when he’s very young; if he gets it at all, he gets it after a long search and a deep conviction. After that it’s truly part of him as long as he lives.

Chapter 3, p. 184

Here, too, was the guide, the beacon, for such times as humanity might be in danger; here was the Guardian of Whom all humans knew — not an exterior force, nor an awesome Watcher in the sky, but a laughing thing with a human heart and a reverence for its human origins, smelling of sweat and new-turned earth rather than suffused with the pale odor of sanctity.

There were a lot of people living in his time who never did latch on to the idea that the curve of technological progress was not a flat slanting line like a diving board, but a geometrical curve like a ski-jump. These wistful and mixed-up souls were always suffering from attacks of belated conservatism, clutching suddenly at this dying thing and that, trying to keep it or bring it back. It wasn’t real conservatism at all, of course, but an unthought longing for the dear old days when one could predict what would be there tomorrow, if not next week. Unable to get the big picture, they welcomed the conveniences, the miniaturization of this and the speed of that, and then were angrily confused when their support of these things changed their world.

Section 11 (p. 33)

You have questions—urgent questions—I know that. And what makes them urgent is that you have in your mind the answers you want to hear. You will be more and more angry if you do not get those answers, but some can’t be given as you would hear them, because they would not be true.

Section 13 (p. 40)

And Charlie asked questions! His unease had long since disappeared, and two of his most deep-dyed characteristics took over: one, the result of his omnivorous, undisciplined, indefatigable reading and picking of brains; second, the great gaping holes this had left in his considerable body of knowledge. Both appeared far more drastic than he had heretofore known; he knew ever so much more than he knew he knew, and he had between five and seven times as much misinformation and ignorance than he had ever dreamed.

Section 19 (p. 59)

As Adam said when his wife fell out of the tree—Eve’s dropping again.

Section 24 (p. 71)

“Now how can you like a man without wanting him?” she demands of herself aloud.
There is no answer. It is an article of faith with her. If you like a man, it has to be because you want him. Whoever heard of it any other way?

Section 32 (p. 101)

Is it men’s disgust of women that makes so many of them treat women with such contempt? Is it that which makes it so easy to point out that the Don Juans and the Lotharios, for all their hunger for women, are often merely trying to see how many women they can punish?

Section 36 (p. 114)

Mankind has in it a crushing need to feel superior. This doesn’t have to bother the very small minority who actually are superior, but it sure troubles the controlling majority who are not. If you can’t be really good at anything, then the only way to be able to prove you are superior is to make someone else inferior. It is this rampaging need in humanity which has, since pre-history, driven a man to stand on the neck of his neighbor, a nation to enslave another, a race to tread on a race. But it is also what men have done to women.
Did they actually find them inferior to begin with, and learn from that to try to feel superior to other things outside—other races, religions, nationalities, occupations?
Or was it the other way around: did men make women inferior for the same reason they tried to dominate the outsider? Which is cause, which effect?

Section 36 (p. 115)

A pig among people is a pig, he tells himself, but a pig among pigs is people.

Section 38 (p. 118)

You cannot be objective about this because you have been indoctrinated, sermonized, drenched, imbued, inculcated and policed on the matter since first you wore blue booties. You come from a time and place in which the maleness of the male, and the femaleness of the female, and the importance of their difference, were matters of almost total preoccupation.

Section 41 (p. 123)

So it is easily seen that the sexual insignes are nothing in themselves, for any of them, in another time and place, might belong to both sexes, the other sex, or neither. In other words, a skirt does not make the social entity, woman. It takes a skirt plus a social attitude to do it.
But all through history, in virtually every culture and country, there has indeed been a “woman’s province” and a “man’s province,” and in most cases the differences between them have been exploited to fantastic, sometimes sickening extremes.Why?

Section 41 (p. 125)

There is in mankind a deep and desperate necessity to feel superior. In any group there are some who genuinely are superior...but it is easy to see that within the parameters of any group, be it culture, club, nation, profession, only a few are really superior; the mass, clearly, are not.
But it is the will of the mass that dictates the mores, initiated though changes may be by individuals or minorities; the individuals or minorities, more often than not, are cut down for their trouble. And if a unit of the mass wants to feel superior, it will find a way. This terrible drive has found expression in many ways, through history—in slavery and genocide, xenophobia and snobbery, race prejudice and sex differentiation. Given a man who, among his fellows, has no real superiority, you are faced with a bedevilled madman who, if superiority is denied him, and he cannot learn one or earn one, will turn on something weaker than himself and make it inferior. The obvious, logical, handiest subject for this inexcusable indignity is his woman.He could not do this to anyone he loved.

Section 41 (p. 126)

There are only three ways of dealing with sex. It may be gratified; it may be repressed; or it may be sublimated. The latter is, through history, often an ideal and frequently a success, but it is always an instability.

Section 41 (p. 128)

Pleasure, the outer edge of ecstasy, was in the dour days of Protestantism, considered sinful in itself, wherever gained; Rome held specifically that any or all sexual pleasure was sinful. And for all this capped volcano produced in terms of bridges and houses, factories and bombs, it gouted from its riven sides a frightful harvest of neurosis. And even where a nation officially discarded the church, the same repressive techniques remained, the same preoccupation with doctrine, filtered through the same mesh of guilt. So sex and religion, the real meaning of human existence, ceased to be meaning and became means; the unbridgeable hostility between the final combatants was the proof of the identity of their aim—the total domination, for the ultimate satisfaction of the will to superiority, of all human minds.

Section 41 (p. 130)

Father-dominated people who form father-dominated cultures have father-religions: a male deity, an authoritative scripture, a strong central government, an intolerance for inquiry and research, a repressive sexual attitude, a deep conservatism (for one does not change what Father built), a rigid demarcation, in dress and conduct, between the sexes, and a profound horror of homosexuality.
Mother-dominated people who form mother-dominated cultures have mother religions: a female deity served by priestesses, a liberal government—one which feeds the masses and succors the helpless—a great tolerance for experimental thought, a permissive attitude toward sex, a hazy boundary between the insignes of the sexes, and a dread of incest.